Recent propagation of smartphones and tablet PCs and introduction of large-capacity multimedia communication have caused an abrupt increase in mobile traffic. Mobile traffic is expected to double every year. Since mobile traffic is mostly transmitted through a base station, telecommunication carriers are facing a serious network load problem. To solve the problem, telecommunication carriers enlarge network equipment in order to handle increasing traffic and rapidly commercialize next-generation mobile communication standards capable of efficiently processing a large amount of traffic, such as mobile WiMAX and LTE (Long Term Evolution). However, to handle traffic which will rapidly increase, other solutions are needed.
Device-to-device (D2D) communication is a distributed communication method for directly transmitting traffic between neighboring nodes without using infrastructure such as base stations. In a D2D communication environment, each node such as a terminal discovers a physically neighboring terminal, establishes a communication session and then transmits traffic. Since D2D communication can solve the traffic overload by distributing traffic concentrated on the base station, D2D is spotlighted as element technology of next-generation mobile communication technology following 4G. For this reason, standard groups such as 3GPP and IEEE promote establishment of D2D communication standards based on LTE-A or Wi-Fi and Qualcomm is developing its own D2D communication technology.
To efficiently use radio resources in an LTE system, a base station needs to recognize a degree to which a terminal wants to transmit data. In the case of uplink, particularly, the amount of data to be transmitted from the terminal needs to be reported to the base station. If the amount of data to be transmitted from the terminal is not reported to the base station, then the base station cannot determine the amount of radio resources to be allocated to the terminal, leading to inefficient radio resource allocation.
To solve this problem, a terminal that intends to transmit data through uplink can report the amount of data to be transmitted on uplink through a buffer status report (BSP). The base station can determine the amount of radio resources to be allocated to the terminal on the basis of the buffer status report received from the terminal.
In D2D communication, a target to which a buffer status of a transmitting terminal is reported is not fixed since D2D communication is communication between terminals rather than communication between a terminal and a base station, distinguished from LTE. Therefore, a buffer status reporting method has not been discussed for D2D communication.
Accordingly, D2D communication still has a problem of inefficient radio resource allocation between a transmitting terminal and a receiving terminal and a problem that the receiving terminal needs to continuously monitor allocated radio resources even after completion of data transmission since the receiving terminal cannot recognize the end time of data transmission from the transmitting terminal